Comparison of divalent ion binding sites in different regulatory proteins: troponin skeletal, cardiac and P-light chains in myosin from rabbit, heart, scallop, arterial and intestinal smooth muscle and from platelets, using Mn as the model ion since it provides structural informaton through bound spectra and proton relaxation times. Comparison of behavior of S-1 and HMM during interaction with actin filaments to determine what properties are modified by double-headedness --distinguishing between specific effects of double headednss and different conformations of active sites. Investigation of all factors that determine the steepness of the calcium switch on troponin since we found the switch to be steeper than explained by fourth power calcium action. BIBLIOGRAPHIC REFERENCES: Marston, S.B. and Weber, A. (1975) The Dissociation Constant of the Actin Heavy Meromyosin Subfragment-1 Complex. Biochemistry 14: 3868. Pemrick, S. and Weber, A. Mechanism of Inhibition of Relaxation of N-ethyl-maleimide Treatment of Myosin, (l976, in press).